Here's a couple more ideas:

1. Is there any way to see if the fuel is surging going into the carb? Either with a temporary fuel or pressure measurement?

2. Might check the plug wires - if one has a pinhole that only arcs when conditions are right that might be a possibility.

3. Carefully examine all of the valve train. Make sure all of the springs are not broken and that they test to correct strength. Also make
sure all of the hardware is there. I had a Chief (I know, different engine) that had a similar problem a while back. After doing the rope
trick on all of the cylinders and checking all of the springs, on reassembly I was missing a washer under one of the valve springs.
Looked all over and decided it wasn't on the engine to begin with. Got a new one and the problem went away. This problem didn't come on until the temperature changed.

Hope this helps.

Maybe just buy a new engine, put it on, see if it solves the surging.

Zzz wrote:Maybe just buy a new engine, put it on, see if it solves the surging.

Haha. Trust me, the thought has crossed my mind...

Several years ago I put new Superior cylinders on a 0-200, ran good until climb out then would loose power. Worked with Superior, too much choke and with heat friction went up dropping RPM. They warranted cylinders. Many years ago my father had 90 in a PA-11 similar problem, A bearing was starting to spin. You didn't change cylinders but might be worth a try to pull it through immediately after shut down and see if it is tight and have crank end clearance, no end clearance is sign of spun bearing. Mag grounding check before of course. I feel for you.

So, an update on this thread. Pulled all the valve springs and they look good. Spark plug leads all test well with a high tension tester. New plugs installed and it didn't help. After run up there is no tightness and still has crank end play. A lot of people stumped on this one.
A new revelation came after the CFI of the flight school that flew it on the past flight is that it happened 4 minutes into flight, not right on the ground, the first occurrence. This was revealed when he came to fill the logbook out a month after the incident. To me this eliminates a few items from a diagnosing stand point.
Needless to say, I've found another running engine and it is going on the plane. Took Zzzs advice. Was just spending to much time and money on a 2100hr engine.

Hi David,

You may be past trying other ideas, but if not... any chance you have an intake leak showing up at those settings, rather than blockage?

UpNorth wrote:Hi David,

You may be past trying other ideas, but if not... any chance you have an intake leak showing up at those settings, rather than blockage?

Hey Rod.
Ya I guess thats possible, but an intake leak should show up as running lean shouldn't it? So leaning the fuel would make it run rougher not smoother. That was my train of thought as well as 2 engine shops. But we could all be wrong.
All the clamps are tight.

Sad to see this problem go undiagnosed.
I am experiencing the same exact problem with my O-200a (Cessna 150).
Seems to be intermittent, and only happens after 5-20 minutes of flight time... sometimes.
Really scary for a student pilot (myself) to deal with power losses on climb out when I'm just trying to learn how to fly.
Ofcourse, it never replicates itself in front of my A&P.
Engine has @900 hours, so unfortunately, dumping the engine for a new one doesn't make financial sense yet. But after having my nerves rattled more than a few times now, I am starting to consider it.
My CFI and I flew the plane home 10 hours after purchasing, then subsequently trained for 15 more hours (25 hours total) before the problem showed itself.
We have been through all the ideas floated previously in this thread.
A/P replaced the carb which was had sloppy linkages and seemed to have a few leaky seals. Lots of carb tuning ensued. Made sense, but virtually no change with the problem.
A/P tested all plugs, wires, checked mags and timing multiple times.
A/P ruled out the valve issues.
A/P found corrision in the fuel tanks, so we replaced both tanks and inspected all fuel lines and flow.

After replacing the tanks, it seemed to fix problem for about 20 hours of training. Today, I'm prepping for my check ride in 2 weeks and it starts acting up again after 3 laps in the pattern.

My CFI seems to be really happy with my flying and I am feeling well prepared for my check ride, but the never ending maintenance costs and my plane constantly trying to kill me has me at my wits end. If I can't figure this out, this may be the end of my recreational flying dreams.


Any further help is appreciated.

If you aren’t already a member, join the Cessna 150 -152 club. They are a excellent resource for anything 150 or O-200 related. https://cessna150152club.org/. Planes suck sometimes, but it’s worth it.

Pete